Smelting ores or the like



Patented Nov. 25, 1924.

LUDWIG HEINRICH DIEHL,

OF DABMSTADT, GERMANY.

SMELTING ORES OR THE LIKE.

N 0 Drawing. Application filed September To all whom it may concern:

Be it known that I, Lunwro I'TEINRICH DrnnL, a subject of Germany, residing in Darmstadt, Germany, have invented certain new and useful Improvements in Smelting Ores or the like (for which I have filed applications in Germany, March 12, 1919, Serial No. D. 35,5 l3 Vii/40 September 15, 1919, Serial No. D. 36,404 VI/lO; Great Britain, March 12, 1920, Serial No. 7,446; July 12, 1920, Serial No. 20,885; Australia, September 9, 1920, Serial No. 17,669; Canada, August 6, 1920, Serial No. 244,985; Italy, August 14, 1920, Serial no. 39,356; Norway, September 29, 1920, Serial No. 21,888; Sweden, August 6, 1920, Serial No. 4,211; India, August 10, 1920, Patent No. 6,081; Mexico, September 3,1920, Patent No. 19,493; Rhodesia, November 6, 1920, Patent No. 1,602; and Spain, October 13, 1920, Patent No. 75,065), of which the following is a specification.

The present invention relates to improvements in the preparation and smelting of ores, roaster-residues, slags, and the like containing iron and zinc, for the separation and recovery of these metals in commercially useful forms.

It is well known that when zinc-bearing iron ores, residues and the like are smelted in blast-furnaces such as are used in making pig-iron, the metallic zinc volatilized from the charge gives rise to deposits and .incrustations in the throat and gas pipes of the furnace, forming obstructions which at times cause great trouble. Sometimes the ZlIlC- penetrates into the oints of the brickwork where, becoming gradually oxidized, it increases in volume and tends to displace the brickwork. Large quantities of zinc bearing iron ores, residues and the like are available which, on account of their containing appreciable quantities of zinc or both zinc and sulphuiyhzwe hitherto been regarded as unsuitable or even worthless for smelting in blast-furnaces The chief objects of the present invention are to prepare such. zinc-bearing materials 1 in a. form chemically and physically suitable tor treatment in the blast-furnace and then by smelting them with suitable addition to separate and recover the iron and zinc without the drawbacks referred to, substantially the whole of the zinc in the charge being volatilized and carried out of the tur- 6, 1921. Serial No. 498,954.

nace by the current of gas as an unohjectionable compound which is recovered as a useful product while the iron is tapped oil? as molten metal to yield pig-iron or other :terrous product of good quality.

According to the invention the raw materialemployed (viz, the ore, roaster-residue, slag or the like, or mixture of such materials, containing iron and zinc, and hereinafter termed ore) is first desulphurized, and it it be too fine t'or blast-furnace work is brought into suitable physical form by sintering, briquetting, or otherwise. Since itmust, when charged into the furnace, contain enough iron to yield molten metal in quantity suflicient to enable the latter to be tapped in the usual way, any deficiency in iron is rectified by the addition of suitable materials, such as iron ore or scrap iron. It is then smelted in the usual manner in a blast-furnace along with the usual reducing and fluxing agent, (coal or coke, limestone and the like) and other materials if desired, and in presence of a chloride. The presence of a chloride is most easily procured by mixing with the charge a chloride in suitable proportions, in which case an alkali chloride, an alkaline earth chloride, zinc chloride,-or a mixture of such chlorides is most suitable, being less easily volatile or decomposable at the temperature of the upper part of the blast furnace than most other chlorides, and being free from metals which might pass into the iron produced and impair its quality. The zinc present in the charge is thus volatilized, probably as chloride or oxychloride, and carried out of the furnace by the gas, while the iron and slag are obtainedin a molten condition free or practically tree from zinc. The iron is tapped off and may be used directly for steel-making, cast into pig-iron, or otherwise utilized. The zinc compound is collected from the gas in anyconvenient manner; it may, for example, be recovered partly in the fine dust and partly in the gaswashing plant, this method havin th advantage that a clean combustible gas, similar to ordinary blast-furnace gas and suitable t'or use in "as-engines or for heating purposes, mav be obtained The nature and proportions of the fuel, tluxing materials and other additions (iii at 1y) in the charge are chosen with regard to \he composition of the ore and kind of iron to be produced, in

the manner well understood in ordinary blast-furnace practice; by suitable selection of these a typical blast-furnace slag, containing only about 0.1 per cent of zinc and adapted to be run off in the usual manner can be obtained.

'The quantity of suitable chloride to be added to the charge depends upon the amount of Zinc present, and may be in the proportion of about 2 atoms of combined chlorine to 1 atom present in the ore. I have discovered, however, that Zinc oxide can be volatilized somewhat readily along with zinc chloride if it be heated together with the latter compound in a current of blast-furnace gas, and that a smaller proportion of chloride than that just mentioned is therefore sufficient for carrying out the process satisfactorily, especially when the charge 18 very rich 1n zinc. The reduction in the proportion of chloride must not be carried too far, since a pronounced shortage of chloride would lead to the volatilization of metallic Zinc and the troubles indicated above would tend to arise in greater or less degree. It is best so to regulate the amount that the zinc product carried out of the furnace contains little or no metallic. zinc; for example the zinc product deposited in the settling ponds of the gaswashing plant should develop therein only a small amount, ifany, of hydrogen gas.

In smelting the ore with the addition of suitable chloride as described, the formation of incrustations in the furnace and pipesis'reduced to a minimum, as the zincbeing in a more volatile form than heretofore'is carried almost entirely into the flue dust or the gas-washers. The volatilized zinc compound while being carried by the gas current is exposed to the action of the lime, alkali and moisture therein;

it is also exposed to the action of alkali in the gas washer-the water in which is normally alkaline and for the purpose of this invention is, if necessary, kept slightly alkaline by. the addition of lime or suitable a lkali-and the zinc is thus collected in the wash-water as basic carbonate or the like, the combined chlorine which was present in the volatilized compound passing into solution as alkali chloride or alkalineearth chloride. Thecrude precipitate, contaminated with coke dust, flue dust and other impurities, may "be allowed to subside in the settling ponds, collected by filtration or otherwise, washed with water to remove soluble substances and then calcined to eliminate combustible and volatile impurities and to render the otherwise comparatively voluminous product denser. It then consists of crude zinc oxide, which may be utilized in any desired manner.

The solutions of chlorides of the a'lkalies or alkaline-earths obtained in the gas-wash ing plant can be evaporated and the concentrated product used as suitable chloride for fresh operations in the furnace.

The invention is particularly applicable to the treatment of the roaster-residues produced from zinciferous pyrites. As is known, the residues obtained on burning such pyrites in roaster furnaces for the manufacture of sulphuric acid retain a fairly large proportion of sulphur, which may be as much as 5 to 8 per cent. I prefer to desulphurize, sinter and smelt such residues in the following manner. The residue is crushed to about one-quarter inch size and roasted (preferably in rotary kilns about 60 metres in length by about 2 to 3 metres in diameter or in other mechanically-operated furnaces) with fuel and a limited supply of air so that a portion say one fourth part-of the ferric oxide present is reduced to ferrous oxide. The enhanced fusibility of the product allows it to become sintered while desulphurization is taking place. The quantities of fuel (coal, coal-dust, coke oil or gas) and of air used are so regulated that the exit gas contains about to 5.5 per cent by volume of S0 6 to 9 per cent of CO and S to 11 per cent of O, and the sulphur in the residue is reduced to 0.5 per cent or less. In order to obtain with a rotary kiln the best results as regards strength of gas, re duction of sulphur contents of the ore and sintering of the latter into a porous material free from dust, the charge should be heated with a long flame to a final temperature at which the material will just begin to fuse and the quantities of fuel and air should be such that about one-fourth part of the ferric oxide is reduced to ferrous oxide. The desul'phurization will then be satisfactory and the sintering will take place more easily than on roasting with a large excess of air. The exit gas can be utilized for the manufacture of sulphuric acid or otherwise; if desired'it can be rendered richer in S0, by adding a proportion of crushed fresh pyri-tes to the charge before the roast ing and sintering operation.

The (lGSllllflllll'lZQCl and sintered product is then smelted with the addition of suitable chloride as already described, the usual reducing, fluxing and other additions being made according to the composition of the ore and the-kind of iron required.

[imam-Me.

metres in diameter having a through-put of about 150 tons of residue 'per 24 hours. For

each metric ton (1000 kilos) of residue there Were used kilos of coal (containing 66.7 per cent of carbon and 1.5 per cent of sulphur) and885 cubic metres of air, yielding 910 cubic metres'of exit gas containing 3.75

- per cent by volume of S0 8.82 per cent of CO and 8.06 per cent of O. The sintered, desulphurized material contained 8.32 per cent of zinc, 0.06 per cent of sulphur, and 44.21 per cent of iron (31.85 per cent as Fe O and 12.35 per cent as FeO). The gas leaving the kiln had a temperature in the dust-chamber of 450500-C. and was suitable for the manufacture of sulphuric acid. The desulphurized material was then smelted with the addition of a suitable chloride and reducing, fluxing and other materials appropriate for the production of pig-iron of the quality (in this case, highmanganese iron) desired. There were used 1308 tons of sintered material, 146 tons of rock salt (sodium chloride),2295 tons of coke, 897 tons of limestone, 278 tons of scrap iron and 278 tons of iron in the form of manganiferous iron ore containing 75 tons of Mn. There were produced 1046 tons of pig-iron (containing no zinc, 3.25 per cent Mn, 1.67 per cent Si, 3.68 per cent C,

0.038 per cent S, and 0.170 per cent P), 1

1125 tons of slag containing 0.10 per cent of zinc, and 158 tons of fine dust containing 21'tons of zinc (existing mainly as oxide, oxychloride or the like). The zinc compound carried in the gas was washedout in the gas-washing plant of the furnace; the product was collected from the settling ponds by filtration, washed and calcined at a low red heat to drive out combined water, carbon dioxide and a small quantity of combined chlorine. It then weighed 125 tons and contained 66.3 per cent of Zn82.5 per cent of ZnO. The flue dust was briquetted and returned to the furnace. The gas from the Washing plant consisted of good, clean, blast-furnace gas suitable for use in the ordinary manner. From the foregoing example it will be seen that the invention affords a practical method of treating roasterresidues so as to effect a clean separation of the valuable constituents thereof, with recovery of the iron, zinc, and, (if desired) the sulphur and combustible gas, all in a commercially useful form, and with simultaneous elimination of blastfurnace slag of the usual type substantially free from zinc.

Having thus described the nature of the said invention and the best means I know of carrying the same into practical effect, I claim 1. The treatment of ores or the like containing iron, zinc and sulphur by desulphurizing them smelting them in a blast-furnace in presence of a chloride along with the appropriate fluxing and other ingredients of a blast-furnace charge, tapping off the mol ten iron produced and collecting by means of alkaline Wash-water the yolatihzed zinclferous material carried out of the furnace by the gases, and washing and calcining the zinci'ferous product.

3. The treatment of the roaster-residue of zinciferous pyrites by roasting it with fuel and a limited supply of air until the subst-antially desulphurized and partly deoxidized product becomes sintered, smelting the sintered product in a blast-furnace along with the appropriate fluXing and other ingredients of a blast furnace charge and with the addition of a chloride in the proportion of approximately 2 atoms of combined chlorine to 1 atom of zinc, tapping off the molten iron produced and collecting the volatilized zinciferous material carried out of the furnace by the gases.

4. The treatment of the roaster-residue of zinciferous pyrites by roasting it with fuel and av limited supply of air until the substantially desulphurized and part-1y deoxidized product becomes sintered, smelting the sintered product in a blast-furnace along with the appropriate fluxing and other ingredients of a blast-furnace charge, and with the addition of a chloride in a proportion which is less than 2 atoms of combined chlorine to 1 atom of zinc and is sufiicient to convert the zinc into an oxychloride substantially free from metallic zinc, tapping off the molten iron produced and col lecting the volatilized zinciferous material carried out of the furnace by the gases.

5. The treatment of the roaster-residue of Zinciferous pyrites by roasting it with fuel and a limited supply of air until the .substantially de-sulphurized and partly deoxidized product becomes sintered, smelting the sintered product in a blast-furnace with addition of the chloride recovered from the wash-water used for collecting the volatilized zinciferous material along with the appropriate fluxing and other ingredients of a blast-furnace charge, tapping off the molten iron produced, collecting by means of alkaline washwater the volatili-zed zinciferous material carried out of the furnace by the gases, washing and calcining the zinciferous product and recovering by evaporation the chloride in the used wash-water.

6. The treatment of the roaster-residue of Zinciferous pyrites by roasting it in a rotary kiln with coal and a limited supply of air until about "one-fourth pairt (if the ferric oxide is cenverted' into aierrous oxide :zmrl the sulphur isweclnceclto-less than 0.5 per cent, the final temperature'loeingthat at which the product just lieginsto 'fuse, smelting wt'he sintere cl IlGSlllPllll-flZBCl material in ablast-furnace :aleng with ch-evapgpropri are fluxiumg and ether ingredients of blastfurnace charge, and With the reddi- 'tion "0 f a: preportionef sodium "chloride sulfieient to "volatilize .the zinc 1 as van =0xyel1l0- ride -suhstanpially free *from metallic Zinc, :-1;a;p.pi1rg off '1 the lmolten iron npro'clu'ced 00lllecting" :hy: means (if. alkaline waslvwater the velatilizecl zineiferous :nmterial earrried 011's 0']? the inrnace by the :ga-ses, and washing and calcining the-zinci l erous product.

7. The manufacture-ef -c1mde-zine oxide :from ores or the hke eenlazumn iron and zine by 'smell'ing-t l-ie-nrin 'a'bzlast turnace in the presence of -Cl1l'0l1Cl6 :al OJTg-AVltll the app rop'rl ate fluxing and other ingredients of a blast;- fn'rnace charge, collecting-by means of alkaline wash-warer the volatilize-d .zineifereus material carried-out of the furnace lay-the ag-zises, and washing'anid calcining thewineif- LUDIVIG \HEIN'RTGH DIE HI 1. 

